1. Field of the Present Invention
The present invention relates to a thermal development photosensitive material. More specifically, it relates to a thermal development photosensitive material suitable for medical diagnoses, industrial photography, printing and COM, and an image-forming method using the material.
2. Description of the Related Art
In recent years, for the sake of environmental conservation and space saving, a decrease in amounts of effluent has been in high demand in the fields of films for medical diagnosis and photolithographic films. Accordingly, technology of thermal development photosensitive materials as films for medical diagnosis and photoengraving films which can be exposed with a laser image setter or a laser imager more efficiently to form a clear black image having high resolution and sharpness has been required. With such thermal development photosensitive materials, a thermal development system which does not need solution-type processing chemicals and which can be handled more easily without environmental pollution can be supplied to clients.
There is also the same demand in the field of general image-forming materials. However, since images for medical diagnoses in particular require minute detailing, a high image quality excellent in sharpness and graininess is needed, and an image with a cool black tone is desired in view of easy diagnosis. Various hard copy systems using pigments and dyes, such as an ink jet printer, electrophotography and the like are currently being distributed as general imaging systems. Nevertheless, these are not satisfactory as an output system of medical images.
A thermal imaging system using an organic silver salt is described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d (Imaging Processes and Materials, Neblette, 8th edition, compiled by J. Sturge, V. Walworth and A. Shepp, chapter 9, p. 279, 1989). Especially, a thermal development photosensitive material generally has a photosensitive layer in which a catalytic amount of a photo-catalyst (for example, a silver halide), a reducing agent, a reducible silver salt (for example, an organic silver salt) and, as required, a color matching agent for controlling the tone of silver are dispersed in a matrix of a binder. After exposure of an image, a thermal development photosensitive material is heated to a high temperature (for example, more than 80xc2x0 C.), and a black silver image is formed by a redox reaction between a reducible silver salt (that acts as an oxidizer) and a reducing agent. The redox reaction is expedited by catalytic activity of a latent image of the silver halide generated through exposure. Accordingly, a black silver image is formed in an exposed area. This is disclosed in a large number of documents including U.S. Pat. No. 2,910,377 and Japanese Patent Publication No. 43-4924.
With the technological innovation and digitalization of recent years, thermal imaging systems with organic silver salts, which have been employed in output systems of medical images, have used a laser as an exposure light source. Further, the type of laser used is generally a semiconductor laser of an infrared wavelength, because laser power can be obtained at low cost.
A pure black tone is desired in an image for medical diagnosis. In these thermal imaging systems with organic silver salts, it is difficult to give a pure black tone, and the tone is controlled with the color matching agent. Nevertheless, the tone controlling has not been satisfactory, and improvement thereof has been called for.
In an infrared-sensitized thermal development photosensitive material, sensitivity is increased by using a hetero-aromatic mercapto compound or a hetero-aromatic disulfide compound as a strong sensitizer. When the amount of the mercapto compound or the disulfide compound is increased, the sensitivity is increased. However, the image tone is changed, and the pure black tone is hard to obtain. Thus, improvement has been called for.
The present invention aims to attain the following upon solving the problems of the related art. That is, the present invention aims to provide a thermal development photosensitive material for use in medical imaging or photolithography which material gives an image with good tone (close to a pure black tone), and an image-forming method using the material.
The present inventors have assiduously conducted investigations to solve the problems, and have consequently found that a desirable thermal development photosensitive material which brings forth predetermined effects can be prepared using a combination of a specific reducing agent and specific compounds. This finding has led to the completion of the present invention.
Approaches to solve the problems are as follows.
The present invention discloses a thermal development photosensitive material having, on one surface of a substrate, at least one photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for silver ions and a binder, the reducing agent including: (a) at least one of polyphenol compounds represented by the following formula (I); and (b) at least one of hindered phenol compounds represented by the following formula (II), wherein a molar addition ratio of the at least one compound represented by formula (II) to the at least one compound represented by formula (I) is from 0.001 to 0.2: 
in which formula R11 and R11xe2x80x2 each independently represents an alkyl group having 1 to 20 carbon atoms; R12 and R12xe2x80x2 each independently represents a hydrogen atom or a substituent that is substitutable to a benzene ring; L represents xe2x80x94Sxe2x80x94 or xe2x80x94CHR13xe2x80x94; R13 represents a hydrogen atom or an optionally substituted alkyl group having 1 to 20 carbon atoms; and X1 and X1xe2x80x2 each independently represents a hydrogen atom or a group that is substitutable to a benzene ring, and: 
in which formula R21 and R22 each independently represents a hydrogen atom, an optionally substituted alkyl group or an optionally substituted acylamino group; neither of R21 and R22 is a 2-hydroxyphenylmethyl group; R21 and R22 are not both hydrogen atoms; R23 represents a hydrogen atom or an optionally substituted alkyl group; and R24 represents a substituent that is substitutable to a benzene ring.
In some embodiments, the present invention is the thermal development photosensitive material, wherein in formula (II), R21 is an optionally substituted alkyl group.
In some embodiments, the present invention is the thermal development photosensitive material, wherein the photosensitive silver halide is infrared-sensitized.
In some embodiments, the present invention is the thermal development photosensitive material, wherein the molar addition ratio of the at least one compound represented by formula (II) to the at least one compound represented by formula (I) is from 0.005 to 0.1.
In some embodiments, the present invention is the thermal development photosensitive material, wherein at least one compound selected from hetero-aromatic compounds and hetero-aromatic disulfide compounds is further contained.
Further, the present invention discloses an image-forming method which includes exposing the thermal development photosensitive material to a laser having an exposure wavelength of 750 nm to 1,400 nm.
Moreover, the present invention discloses an image-forming method which includes processing the thermal development photosensitive material for a thermal development time of 5 to 20 seconds.
The present invention is described in detail below.
A reducing agent for silver ions to be used in the present invention is described below.
The thermal development photosensitive material of the present invention contains a reducing agent for an organic silver salt. The reducing agent for the organic silver salt may be any material (preferably an organic material) that reduces silver ions to metallic silver. Such a reducing agent is described in Japanese Patent Application Laid-Open (JP-A) No. 11-65021, paragraphs [0043] to [0045] and European Patent Laid-Open No. 0803764A1, page 7, line 34 to page 18, line 12.
In the present invention, a bisphenol reducing agent is preferable as the reducing agent, and at least one of compounds represented by formula (I) is contained. 
In formula (I), R11 and R11xe2x80x2 each independently represents an alkyl group having 1 to 20 carbon atoms; R12 and R12xe2x80x2 each independently represents a hydrogen atom or a substituent that can be substituted to a benzene ring; L represents xe2x80x94Sxe2x80x94 or xe2x80x94CHR13xe2x80x94; R13 represents a hydrogen atom or an optionally substituted alkyl group having 1 to 20 carbon atoms; and X1 and X1xe2x80x2 each independently represents a hydrogen atom or a group replaceable in a benzene ring.
Formula (I) is described in detail below.
R11 and R11xe2x80x2 each independently represents an alkyl group having 1 to 20 carbon atoms, which group may be substituted or unsubstituted. The substituent is not particularly limited. Preferable examples thereof include aryl, hydroxy, alkoxy, aryloxy, alkylthio, arylthio, acylamino, sulfonamide, sulfonyl, phosphoryl, acyl, carbamoyl and ester groups and halogen atoms.
The alkyl group is more preferably a secondary or tertiary alkyl group having 3 to 15 carbon atoms, especially preferably a tertiary alkyl group having 4 to 12 carbon atoms. Specific examples thereof include isopropyl, isobutyl, t-butyl, t-amyl, t-octyl, cyclohexyl, cyclopentyl, 1-methylcyclohexyl and 1-methylcyclopropyl groups. Of these, t-butyl, t-amyl and 1-methylcyclohexyl groups are preferable, and a t-butyl group is most preferable.
R12 and R12xe2x80x2 each independently represents a hydrogen atom or a substituent that can be substituted to a benzene ring. Preferable examples of the substituent replaceable in the benzene ring include an alkyl group, an aryl group, a halogen atom, an alkoxy group and an acylamino group.
R12 and R12xe2x80x2 are preferably an alkyl group having 1 to 20 carbon atoms. Specific examples thereof include methyl, ethyl, propyl, butyl, isopropyl, t-butyl, t-amyl, cyclohexyl, 1-methylcyclohexyl, benzyl, methoxymethyl and methoxyethyl groups. Methyl, ethyl, propyl, isopropyl and t-butyl groups are preferable.
When R13, to be described later, is a hydrogen atom, R12 and R12xe2x80x2 are more preferably an alkyl group having 2 to 5 carbon atoms. Specifically, ethyl and propyl groups are more preferable, and an ethyl group is most preferable.
When R13 is a primary or secondary alkyl group having 1 to 8 carbon atoms, R12 and R12xe2x80x2 are most preferably a methyl group. The primary or secondary alkyl group having 1 to 8 carbon atoms is described in the section on R13.
X1 and X1xe2x80x2 each independently represents a hydrogen atom or a group replaceable in a benzene ring. Preferable examples of the group replaceable in the benzene ring include an alkyl group, an aryl group, a halogen atom, an alkoxy group and an acylamino group.
X1 and X1xe2x80x2 are each preferably a hydrogen atom, a halogen atom or an alkyl group, and most preferably a hydrogen atom.
L represents xe2x80x94Sxe2x80x94 or xe2x80x94CHR13xe2x80x94. R13 represents a hydrogen atom or an optionally substituted alkyl group having 1 to 20 carbon atoms. Examples of a substituent in the alkyl group include halogen atoms and alkoxy, alkylthio, aryloxy, arylthio, acylamino, sulfonamide, sulfonyl, phosphoryl, oxycarbonyl, carbamoyl and sulfamoyl groups.
Specific examples of the unsubstituted alkyl group include methyl, ethyl, propyl, butyl, heptyl, undecyl, isopropyl, 1-ethylpentyl and 2,4,4-trimethylpentyl groups.
L is preferably xe2x80x94CHR13xe2x80x94.
R13 is preferably a hydrogen atom or an alkyl group having 1 to 15 carbon atoms. A hydrogen atom or an alkyl group having 1 to 10 carbon atoms is more preferable. Specifically, a hydrogen atom and methyl, ethyl, propyl, isopropyl and 2,4,4-trimethylpentyl groups are preferable. A hydrogen atom and methyl, propyl and isopropyl groups are more preferable.
As the primary or secondary alkyl group having 1 to 8 carbon atoms as described for R12 and R12xe2x80x2, methyl, ethyl, propyl and isopropyl groups are more preferable, and methyl, ethyl and propyl groups are further preferable.
When, R11, R11xe2x80x2, R12 and R12xe2x80x2 are all methyl groups, R13 is preferably a secondary alkyl group. As the secondary alkyl group, isopropyl, isobutyl and 1-ethylpentyl groups are preferable, and an isopropyl group is more preferable.
Specific examples of compounds represented by formula (I) as the reducing agent of the present invention are shown below. However, the present invention is not limited thereto. 
In the present invention, the amount of the compound represented by formula (I) is preferably 0.01 to 5.0 g/m2, more preferably 0.1 to 3.0 g/m2. The amount is also preferably 5 to 50 mol %, more preferably 10 to 40 mol % for each mol of silver on a surface having an imaging layer.
It is advisable that the compound represented by formula (I) is contained in the imaging layer.
The compound represented by formula (I) may be incorporated in a coating solution by any of a solution method, an emulsion dispersion method and a solid fine grain dispersion method, and incorporated in a photosensitive material.
As a well-known emulsion dispersion method, a method can be mentioned in which the compound is dissolved using an oil such as dibutyl phthalate, tricresyl phosphate, glyceryl triacetate or diethyl phthalate or a co-solvent such as ethyl acetate or cyclohexanone, and an emulsion dispersion is mechanically produced.
As the solid fine grain dispersion method, a method can be mentioned in which a powder of the compound represented by formula (I) is dispersed in an appropriate solvent such as water with a ball mill, a colloid mill, a vibration ball mill, a sand mill, a jet mill, a roller mill or ultrasound to form a solid dispersion. At this time, a protective colloid (for example, polyvinyl alcohol) and a surfactant (for example, an anionic surfactant such as sodium triisopropylnaphthalenesulfonate (in which three isopropyl groups have different substitution positions)) may be used. A water dispersion may contain a preservative (for example, benzoisothiazolinone sodium salt).
In the present invention, at least one of hindered phenol compounds represented by formula (II) is also contained. 
In formula (II), R21 and R22 each independently represents a hydrogen atom, an alkyl group or an acylamino group; R21 and R22 are not 2-hydroxyphenylmethyl groups, nor are R21 and R22 both hydrogen atoms at the same time; R23 represents a hydrogen atom or an optionally substituted alkyl group; and R24 represents a substituent that can be substituted to a benzene ring.
Formula (II) is described in detail below.
When R21 is an alkyl group, an alkyl group having 1 to 30 carbon atoms is preferable, and an alkyl group having 1 to 10 carbon atoms is more preferable.
The alkyl group may be an optionally substituted alkyl group. Specifically, as the unsubstituted alkyl group, methyl, ethyl, butyl, octyl, isopropyl, t-butyl, t-octyl, t-amyl, sec-butyl, cyclohexyl and 1-methylcyclohexyl groups are preferable. A group sterically greater than an isopropyl group is more preferable, examples thereof being isononyl, t-butyl, t-amyl, t-octyl, cyclohexyl, 1-methylcyclohexyl and adamantyl groups. Of these, t-butyl, t-octyl and t-amyl groups, which are tertiary alkyl groups, are especially preferable.
When the alkyl group is a substituted alkyl group, examples of the substituent include halogen atoms and aryl, alkoxy, amino, acyl, acylamino, alkylthio, arylthio, sulfonamide, acyloxy, oxycarbonyl, carbamoyl, sulfamoyl, sulfonyl and phosphoryl groups.
When R22 is an alkyl group, an alkyl group having 1 to 30 carbon atoms is preferable, and an unsubstituted alkyl group having 1 to 24 carbon atoms is more preferable.
The alkyl group may be an optionally substituted alkyl group. Preferable examples of the unsubstituted alkyl group include methyl, ethyl, butyl, octyl, isopropyl, t-butyl, t-octyl, t-amyl, sec-butyl, cyclohexyl and 1-methylcyclohexyl groups.
Examples of the substituent are the same as for R21.
When R21 or R22 is an acylamino group, an acylamino group having 1 to 30 carbon atoms is preferable, and an acylamino group having 1 to 10 carbon atoms is more preferable.
The acylamino group may be unsubstituted or substituted. Specific examples thereof include acetylamino, alkoxyacetylamino and aryloxyacetylamino groups.
For R21, among a hydrogen atom, an alkyl group and an acylamino group, an alkyl group is preferable.
For R22, among a hydrogen atom, an alkyl group and an acylamino group, a hydrogen atom and an unsubstituted alkyl group having 1 to 24 carbon atoms are preferable. Specific examples thereof include methyl, isopropyl and t-butyl groups.
R21 and R22 cannot be 2-hydroxyphenylmethyl groups, nor can they both be hydrogen atoms at the same time.
R23 represents a hydrogen atom or an alkyl group. Among these, a hydrogen atom or an alkyl group having 1 to 30 carbon atoms is preferable, and a hydrogen atom or an unsubstituted alkyl group having 1 to 24 carbon atoms is more preferable. Description of the alkyl group is the same as for R22. Specific examples thereof include methyl, isopropyl and t-butyl groups.
It is preferable that one of R22 and R23 is a hydrogen atom.
R24 represents a group replaceable in a benzene ring, which is the same as those described for R12 and R12xe2x80x2 in the compounds of formula (I). Preferable examples of the group of R24 include a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, and an oxycarbonyl group having 2 to 30 carbon atoms. An alkyl group having 1 to 24 carbon atoms is more preferable. Examples of the substituent of the substituted alkyl group include aryl, amino, alkoxy, oxycarbonyl, acylamino, acyloxy, imido and ureido groups. Aryl, amino, oxycarbonyl and alkoxy groups are preferable.
Of the compounds of formula (II), a preferable structure is represented by formula (III). 
R31, R32, R33 and R34 each independently represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. An alkyl group having 1 to 10 carbon atoms is preferable. The substituent of the substituted alkyl group is not particularly limited. Preferable examples thereof include aryl, hydroxy, alkoxy, aryloxy, alkylthio, arylthio, acylamino, sulfonamide, sulfonyl, phosphoryl, acyl, carbamoyl and ester groups, and halogen atoms. It is preferable that at least one group sterically greater than an isopropyl group (for example, isononyl, t-butyl, t-amyl, t-octyl, cyclohexyl, 1-methylcyclohexyl and adamantyl groups) is present. It is more preferable that at least two such groups are present. As a group which is sterically greater than an isopropyl group, t-butyl, t-octyl and t-amyl groups, which are tertiary alkyl groups, are especially preferable. L is the same as described for the compounds of formula (I).
Specific examples of the compounds of formulas (II) and (III) in the present invention are shown below. However, these are not limiting. 
The compound represented by formula (II) or (III) can be added by the same methods as the compound represented by formula (I). It may be incorporated in a coating solution by any of a solution method, an emulsion dispersion method and a solid fine grain dispersion method, and incorporated in the photosensitive material.
A ratio of the compound of formula (I) (a polyphenol bound in the o-position) and the compound of formula (II) or formula (III) (a hindered phenol compound) (amount of the compound of formula (II) or (III)(mol)/amount of the compound of formula (I)(mol)) is 0.001 to 0.2, preferably 0.005 to 0.1, and more preferably 0.008 to 0.05.
It is advisable that the compounds of formulas (I) and (II) or (III) are incorporated in an imaging layer containing an organic silver salt. It is also possible that one thereof is incorporated in an imaging layer and the other in a non-imaging layer adjacent thereto, or that both compounds are incorporated in a non-imaging layer. Further, when the imaging layer is structured of plural layers, the compounds may be incorporated in separate layers.
In the thermal development photosensitive material of the present invention, phenol derivatives represented by formula (A) described in Japanese Patent Application No. 11-73951 are preferably used as a development accelerator.
When the reducing agent in the present invention has an aromatic hydroxyl group (xe2x80x94OH), especially if it is a bisphenol, it is advisable to use a non-reducible compound having a group capable of forming a hydrogen bond in combination with this group. Examples of the group capable of forming a hydrogen bond with a hydroxyl group or an amino group include phosphoryl, sulfoxide, sulfonyl, carbonyl, amide, ester, urethane, ureido, tertiary amino and nitrogen-containing aromatic groups. Preferable are compounds having a phosphoryl group, a sulfoxide group, an aminde group (free from  greater than Nxe2x80x94H and blocked like  greater than Nxe2x80x94Ra (Ra is a substituent except H)), an urethane group (free from  greater than Nxe2x80x94H and blocked in the manner  greater than Nxe2x80x94Ra (Ra is a substituent that is not H)) or a ureido group (free from  greater than Nxe2x80x94H and blocked in the manner  greater than Nxe2x80x94Ra).
In the present invention, especially preferable examples of the hydrogen-bonding compounds are compounds represented by formula (A). 
In formula (A), R41 to R43 each independently represents an alkyl, aryl, alkoxy, aryloxy, amino or heterocyclic group. These groups may be unsubstituted or substituted. When any of R41 to R43 is a substituted group, examples of the substituent include halogen atoms and alkyl, aryl, alkoxy, amino, acyl, acylamino, alkylthio, arylthio, sulfonamide, acyloxy, oxycarbonyl, carbamoyl, sulfamoyl, sulfonyl and phosphoryl groups. Alkyl and aryl groups are preferable. Specific examples thereof include methyl, ethyl, isopropyl, t-butyl, t-octyl, phenyl, 4-alkoxyphenyl and 4-acyloxyphenyl groups.
Specific examples of alkyl groups of R41 to R43 include methyl, ethyl, butyl, octyl, dodecyl, isopropyl, t-butyl, t-amyl, t-octyl, cyclohexyl, 1-methylcyclohexyl, benzyl, phenetyl and 2-phenoxypropyl groups.
Examples of aryl groups of R41 to R43 include phenyl, cresyl, xylyl, naphthyl, 4-t-butylphenyl, 4-t-octylphenyl, 4-anisidyl and 3,5-dichlorophenyl groups. Phenyl and 4-t-butylphenyl groups are preferable, and a 4-t-butylphenyl group is especially preferable.
Examples of alkoxy groups of R41 to R43 include methoxy, ethoxy, butoxy, octyloxy, 2-ethylhexyloxy, 3,5,5-trimethylhexyloxy, dodecyloxy, cyclohexyloxy, 4-methylcyclohexyloxy and benzyloxy groups.
Examples of aryloxy groups of R41 to R43 include phenoxy, cresyloxy, isopropylphenoxy, 4-t-butylphenoxy, naphthoxy and biphenyloxy groups.
Examples of amino groups of R41 to R43 include dimethylamino, diethylamino, dibutylamino, dioctylamino, N-methyl-N-hexylamino, dicyclohexylamino, diphenylamino and N-methyl-N-phenylamino groups.
Examples of heterocyclic groups of R41 to R43 include pyridyl, pyrimidyl and triazinyl groups.
As R41 to R43, alkyl, aryl, alkoxy and aryloxy groups are preferable. In view of the effects of the present invention, it is preferable that at least one of R41 to R43 is an alkyl group or an aryl group, and it is more preferable that at least two of R41 to R43 are alkyl or aryl groups. R41 to R43 are preferably all the same group because then the compound can be procured at low cost.
Specific examples of hydrogen-bonding compounds such as the compounds of formula (A) in the present invention are shown below. However, the present invention is not limited thereto. 
Specific examples of the hydrogen-bonding compounds include, in addition to the above compounds, those described in Japanese Patent Application Nos. 2000-192191 and 2000-194811.
The compound of formula (A) of the present invention, like the reducing agent, can be incorporated in a coating solution in the form of a solution, an emulsion dispersion or a solid fine grain dispersion, and used in the photosensitive material. The compound of the present invention forms a hydrogen-bonding complex with a compound having a phenolic hydroxyl group or an amino group in a solution state, and can be isolated in a crystalline state as the complex by combination between the reducing agent and the compound of formula (A) of the present invention. For obtaining stable performance, it is especially preferable that the thus-isolated crystalline powder is used as a solid fine grain dispersion. Further, a method in which the reducing agent and the compound of formula (A) of the present invention are mixed in powdery form and the complex is formed in the dispersion using an appropriate dispersing agent with a sand grinder mill can be preferably used.
In the present invention, the amount of the compound of formula (A) is preferably 1 to 200 mol %, more preferably 10 to 150 mol %, and further preferably 30 to 100 mol % relative to the reducing agent.
The non-photosensitive organic silver salt used in the present invention is described below.
The thermal development photosensitive material of the present invention contains a non-photosensitive organic silver salt (hereinafter sometimes referred to simply as xe2x80x9corganic silver saltxe2x80x9d). Although the organic silver salt is relatively stable to light, it is a silver salt that forms a silver image when heated to 80xc2x0 C. or more in the presence of an exposed photocatalyst (photosensitive silver halide latent image) and the reducing agent. The organic silver salt may be any organic material that contains a source capable of reducing silver ions. Such non-photosensitive organic silver salts are described in JP-A No. 10-62899, paragraphs [0048] and [0049], European Patent Laid-Open No. 0803764A1, page 18, line 24 to page 19, line 37, European Patent Laid-Open No. 0962812A1, and JP-A Nos. 11-349591, 2000-7683 and 2000-72711. An organic acid silver salt is preferable, and a long-chain aliphatic carboxylic acid silver salt (having 10 to 30 carbon atoms, preferably 15 to 28 carbon atoms) is especially preferable. Preferable examples of the organic silver salt include silver behenate, silver arachidate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate and mixtures thereof. In the present invention, among these organic silver salts, an organic acid salt containing 75 mol % or more of silver behenate is preferable.
The form of the organic silver salt that can be used in the present invention is not particularly limited. Preferable examples of the form are acicular, bar-shaped, tabular and flaky forms. The acicular and flaky forms are especially preferable. The flaky form is especially preferable.
In the present specification, a flaky organic silver salt is defined as follows. The organic acid silver salt is observed with an electron microscope, and the form of the organic acid silver salt grain is deemed to approximate to a rectangular solid. Sides of this rectangular solid are designated a, b and c in order from the shortest side (c may be the same as b). At this time, a value x is calculated as follows from the shorter values a and b.
x=b/a 
In this manner, x is calculated for 200 grains. If the average value of x meets the relation x (average)xe2x89xa71.5, the form can be regarded as flaky. Preferable is 30xe2x89xa7x (average)xe2x89xa71.5. More preferable is 20xe2x89xa7x (average)xe2x89xa72.0. In the acicular form, 1xe2x89xa7x (average)xe2x89xa71.5.
In flaky grains, a can be regarded as a thickness of a tabular grain in which a surface having sides b and c is a main plane. The average of a is preferably from 0.01 xcexcm to 0.23 xcexcm, more preferably from 0.11 xcexcm to 0.20 xcexcm. The average of c/b is preferably from 1 to 6, more preferably from 1.05 to 4, further preferably from 1.1 to 3, and especially preferably from 1.1 to 2.
A grain size distribution of the organic silver salt is preferably monodisperse. In xe2x80x9cmonodispersionxe2x80x9d, a percent value calculated by dividing a standard deviation of the length of a short axis or a long axis by the short axis or the long axis is preferably 100% or less, more preferably 80% or less, and further preferably 50% or less. The form of the organic silver salt can be measured from a transmission electron microscope image of the organic silver salt dispersion. As another method of measuring monodispersion property, there is a method in which the standard deviation of the volume weighted average diameter of the organic silver salt is measured. A percent value of that value divided by the volume weighted average diameter (fluctuation coefficient) is preferably 100% or less, more preferably 80% or less, further preferably 50% or less. This can be found from a grain size (volume weighted average diameter) obtained by, for example, irradiating the organic silver salt dispersed in a solution with a laser beam and calculating an autocorrelation function of fluctuation of scattered light relative to change of time.
Preparation of the organic acid silver salt used in the present invention and a dispersion thereof can be conducted by known methods referring to, for example, JP-A No. 10-62899, European Patent Laid-Open Nos. 0803763A1 and 0962812A1, JP-A Nos. 11-349591, 2000-7683 and 2000-72711 and Japanese Patent Application Nos. 11-348228 to 11-348230, 11-203413, 2000-90093, 2000-195621, 2000-191226, 2000-213813, 2000-214155 and 2000-191226.
If a photosensitive silver salt is present when the organic silver salt is dispersed, fogging increases, which notably decreases sensitivity. Accordingly, it is preferable that photosensitive silver salt is substantially absent at the time of dispersion. In the present invention, the amount of photosensitive silver salt in the water dispersion is 0.1 mol % or less per mol of the organic acid silver salt in the dispersion, and deliberate addition of the photosensitive silver salt is not conducted.
In the present invention, the photosensitive material can be prepared by mixing the organic silver salt water dispersion with the photosensitive silver salt water dispersion. A mixing ratio of the organic silver salt and the photosensitive silver salt can be selected according to purposes. The ratio of the photosensitive silver salt to the organic silver salt is preferably 1 to 30 mol %, more preferably 3 to 20 mol %, and especially preferably 5 to 15 mol %. A method of mixing at least two organic silver salt water dispersions with at least two photosensitive silver salt water dispersions is preferably used for adjusting photographic characteristics.
The organic silver salt of the present invention can be used in a desired amount. It is preferably 0.1 to 5 g/m2, more preferably 1 to 3 g/m2, in terms of an amount of silver.
A photosensitive silver halide used in the present invention is described below.
The thermal development photosensitive material of the present invention contains the photosensitive silver halide. The photosensitive silver halide is not particularly limited as a halogen composition, and silver chloride, silver chlorobromide, silver bromide, silver iodobromide and silver iodochloride are usable. Of these, silver bromide and silver iodobromide are preferable. The distribution of the halogen composition in grains may be uniform, or the halogen composition may vary stepwise or continuously. Further, silver halide grains having a core/shell structure can be preferably used. The core/shell structure is preferably a 2- to 5-layer structure, more preferably a 2- to 4-layer structure. Moreover, a technique in which silver bromide is localized on the surface of a silver chloride or silver chlorobromide grain can also be preferably used.
Methods of forming the photosensitive silver halide are well known to those skilled in the art. Examples thereof include methods described in Research Disclosure No. 17029, June 1978 and U.S. Pat. No. 3,700,458. Specifically, a method can be employed in which a silver-donating compound and a halogen-donating compound are added to a gelatin or other polymer solution to form the photosensitive silver halide, which is then mixed with the organic silver salt. Further, a method described in JP-A No. 11-119374, paragraphs [0217] to [0224], and methods described in Japanese Patent Application Nos. 11-98708 and 2000-42336 are also desirable.
A smaller grain size of the photosensitive silver halide is preferable for suppressing cloudiness after imaging. Specifically, it is preferably 0.20 xcexcm or less, more preferably from 0.01 xcexcm to 0.15 xcexcm, and further preferably from 0.02 xcexcm to 0.12 xcexcm. The grain size as referred to here means a diameter calculated for a circular image having the same area as a projected area of a silver halide grain (projected area of a main plane in the case of tabular grains).
With respect to form of the silver halide grains, cubic grains, octahedral grains, tabular grains, spherical grains, bar-like grains and potato-like grains can be listed. In the present invention, cubic grains are preferable. Silver halide grains having round corners can also be preferably used. A mirror index of the outer surface of the photosensitive silver halide grains is not particularly limited. It is preferable that a ratio of a [100] surface, which has a high spectral sensitization efficiency when adsorbing a spectral sensitization coloring matter, is high. This ratio is preferably 50% or more, more preferably 65% or more, and further preferably 80% or more. The mirror index ratio of the [100] surface can be found by a method using adsorption dependence of [111] and [100] surfaces in adsorption of sensitization coloring matter, as described by T. Tani, J. Imaging Sci., 29, 165 (1985).
In the present invention, silver halide grains in which a hexacyano metal complex is present on the outermost surface of the grains are preferable. Examples of the hexacyano metal complex include [Fe(CN)6]4xe2x88x92, [Fe(CN)6]3xe2x88x92, [Ru(CN)6]4xe2x88x92, [Os(CN)6]4xe2x88x92, [Co(CN)6]3xe2x88x92, [Rh(CN)6]3xe2x88x92, [Ir(CN)6]3xe2x88x92, [Cr(CN)6]3xe2x88x92 and [Re(CN)6]3, xe2x88x92. In the present invention, hexacyano Fe complexes are preferable.
The hexacyano metal complex is present in an aqueous solution in the form of ions, so counter cations are not required. It is, however, advisable to use an alkali metal ion, such as a sodium ion, a potassium ion, a rubidium ion, a cesium ion or a lithium ion, an ammonium ion or an alkylammonium ion (such as a tetramethylammonium ion, a tetraethylammonium ion, a tetrapropylammonium ion or a tetra(n-butyl)ammonium ion) which is easily miscible with water and suited for precipitation of a silver halide emulsion.
The hexacyano metal complex can be added by being mixed with water, a mixed solvent of water and an appropriate organic solvent that is miscible with water (for example, alcohols, ethers, glycols, ketones, esters and amides), or gelatin.
The amount of the hexacyano metal complex is preferably from 1xc3x9710xe2x88x925 mol to 1xc3x9710xe2x88x922, more preferably from 1xc3x9710xe2x88x924 mol to 1xc3x9710xe2x88x923 mol, per mol of silver.
For the hexacyano metal complex to be present on the outermost surface of the silver halide grains, the hexacyano metal complex is directly added from a time after finishing addition of a silver nitrate aqueous solution used in forming the grains till a chemical sensitization step of conducting chalcogen sensitization such as sulfur sensitization, selenium sensitization or tellurium sensitization, or noble metal sensitization such as gold sensitization. That is, the complex is added before completion of a charging step, during a water-washing step, during a dispersing step or before a chemical sensitization step. In order not to further grow the silver halide grains, it is preferable to add the hexacyano metal complex soon after formation of the grains, and it is more preferable to add the same before completion of a charging step.
The addition of the hexacyano metal complex may be started after 96% by mass of the total amount of silver nitrate has been added to form the grains. It is preferable to start after 98% by mass of the same has been added. It is especially preferable to start after 99% by mass of the same has been added.
When the hexacyano metal complex is added after the addition of the silver nitrate aqueous solution and just before completing formation of the grains, it can be adsorbed on the outermost surfaces of the silver halide grains, and most of the grains form sparingly-soluble salts with silver ions present on the surfaces of grains. Since a hexacyano iron (II) silver salt is more sparingly soluble than AgI, re-dissolution of the grains can be prevented, and silver halide grains having a small grain size can be prepared.
The photosensitive silver halide grains of the present invention can contain metals of Groups 8 to 10 in the periodic table (of groups designated 1 to 18) or complexes of these metals. As the metals of Groups 8 to 10, or center metals of the metal complexes, rhodium, ruthenium and iridium are preferable. The metal complexes may be used singly, or complexes of the same metals or of different metals may be used in combination. The content thereof is preferably 1xc3x9710xe2x88x929 to 1xc3x9710xe2x88x923 mol per mol of silver. The noble metals or metal complexes and addition methods thereof are described in JP-A No. 7-225449, JP-A No. 11-65021, paragraphs [0018] to [0024], and JP-A No. 11-119374, paragraphs [0227] to [0240].
Metal atoms (for example, [Fe(CN)6]4xe2x88x92) that can be contained in the silver halide grains used in the present invention, a desalting method of a silver halide emulsion and a chemical sensitization method are described in, for example, JP-A No. 11-84574, paragraphs [0046] to [0050], JP-A No. 11-65021, paragraphs [0025] to [0031] and JP-A No. 11-119374, paragraphs [0242] to [0250].
It is advisable that the photosensitive silver halide grains in the present invention are chemically sensitized by a sulfur sensitization method, a selenium sensitization method or a tellurium sensitization method. As a compound preferably used in the sulfur sensitization method, the selenium sensitization method or the tellurium sensitization method, known compounds, for example, compounds described in JP-A No. 7-128768, can be used. In the present invention, tellurium sensitization is preferable, and compounds described in JP-A No. 11-65021, paragraph [0030], and compounds represented by formulas (II), (III) and (IV) of JP-A No. 5-313284 are more preferable.
In the present invention, the chemical sensitization can be conducted at any stage after formation of the grains and before coating. It can be conducted after desalting, (1) before spectral sensitization, (2) simultaneously with spectral sensitization, (3) after spectral sensitization or (4) just before coating. Especially, it is preferable to conduct the same after spectral sensitization.
The amount of a sulfur, selenium or tellurium sensitizer used in the present invention varies with the silver halide grains used and chemical ageing conditions. The amount is 10xe2x88x928 to 10xe2x88x922 mol, preferably 10xe2x88x927 to 10xe2x88x923 mol, per mol of silver halide. Conditions of the chemical sensitization in the present invention are not particularly limited. A pH value is 5 to 8, pAg is 6 to 11, and temperature is around 40xc2x0 C. to 95xc2x0 C.
A thiosulfonic acid compound may be added to the silver halide emulsion used in the present invention by a method indicated in European Patent Laid-Open No. 293,917.
With respect to the photosensitive silver halide emulsion in the photosensitive material used in the present invention, one type alone or a combination of two or more types (for example, compounds different in average grain size, compounds different in halogen composition, compounds different in crystal habit or compounds different in conditions of chemical sensitization) may be used. The use of plural photosensitive silver halides different in sensitivity enables adjustment of gradation. Techniques with such compounds are described in JP-A Nos. 57-119341, 53-106125, 47-3929, 48-55730, 46-5187, 50-73627 and 57-150841, etc. With respect to differences in sensitivity, it is preferable to provide a difference of 0.2 logE or more in each emulsion.
The amount of the photosensitive silver halide is preferably 0.03 to 0.6 g/m2, more preferably 0.07 to 0.4 g/m2, and most preferably 0.05 to 0.3 g/m2, in terms of a coating silver amount for 1 m2 of the photosensitive material. Further, the amount of the photosensitive silver halide is preferably from 0.01 to 0.5 mol, more preferably from 0.02 to 0.3 mol, per mol of the organic silver salt.
With respect to method and conditions when mixing the separately formed photosensitive silver halide and organic silver salt, there are a method in which the separately formed silver halide grains and organic silver salt are mixed with a high-speed stirrer, a ball mill, a sand mill, a colloid mill, a vibration mill or a homogenizer, and a method in which the already formed photosensitive silver halide is mixed in at any stage during preparation of the organic silver salt. The method is not particularly limited so long as the effects of the present invention are satisfactorily brought forth. Further, a method in which at least two organic silver salt water dispersions and at least two photosensitive silver salt water dispersions are mixed is preferable for adjusting photographic characteristics.
A time to add the silver halide of the present invention to an imaging layer coating solution is from 180 minutes before coating till just before coating, preferably from 60 minutes to 10 seconds before coating. A mixing method and conditions are not particularly limited so long as the effects of the present invention are satisfactorily brought forth. Specific examples of the mixing method include a method of mixing in a tank in which an average retention time calculated from an addition flow rate and amount of solution fed to a coater becomes a desired time, and a method using a static mixer as described in chapter 8 of xe2x80x9cLiquid Mixing Technologyxe2x80x9d, N. Harnby, M. F. Edwards and A. W. Nienow, translated by Takahashi K. (Nikkan Kogyo Shinbunsha, 1989).
As a gelatin contained in the photosensitive silver halide emulsion used in the present invention, various gelatins are usable. For maintaining a good dispersion state of the photosensitive silver halide emulsion in an organic silver salt-containing coating solution, low-molecular gelatins, having a molecular weight of 500 to 60,000, are preferably used. These low-molecular gelatins may be used in forming grains or during dispersion after a desalting treatment. It is preferable to use them during the dispersion after the desalting treatment.
It is advisable that the thermal development photosensitive material of the present invention is infrared-sensitized. xe2x80x9cInfrared-sensitizedxe2x80x9d means that the photosensitive silver halide is spectrally sensitized to a wavelength zone of 750 nm to 1,400 nm with a sensitization coloring matter. As the sensitization coloring matter, known compounds can be used. The material can be spectrally sensitized advantageously with various known coloring matters such as cyanine, merocyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene coloring matters. Useful cyanine coloring matters are, for example, those having basic nuclei, such as a thiazoline nucleus, an oxazoline nucleus, a pyrroline nucleus, a pyridine nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Preferable useful merocyanine coloring matters are those having, in addition to the basic nuclei, acid nuclei, such as a thiohydantoin nucleus, a rhodamine nucleus, an oxazolidinedione nucleus, a thiazolinedione nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malononitrile nucleus and a pyrazolone nucleus. Of the cyanine and merocyanine coloring matters, those having an imino group or a carboxyl group are especially effective. The coloring matters can be suitably selected from known coloring matters described in U.S. Pat. Nos. 3,761,279, 3,719,495 and 3,877,943, British Patent Nos. 1,466,291, 1,469,117 and 1,422,057, Japanese Patent Publication Nos. 3-10391 and 6-52387 and JP-A Nos. 5-341432, 6-194781 and 6-301141.
These sensitization coloring matters may be used either singly or in combination. A time to add the sensitization coloring matter to the silver halide emulsion in the present invention is preferably from after desalting till coating, more preferably from after desalting till before starting chemical ageing.
The amount of the sensitization coloring matter in the present invention can be a desired amount according to properties such as sensitivity and fogging. It is preferably 10xe2x88x926 to 1 mol, more preferably 10xe2x88x924 to 10xe2x88x921 mol, per mol of the silver halide in the photosensitive layer.
In order to improve spectral sensitization efficiency, a strong color sensitizer can be used in the present invention. As the strong color sensitizer used in the present invention, compounds described in European Patent Laid-Open No. 587,338, U.S. Pat. Nos. 3,877,943 and 4,873,184 and JP-A Nos. 5-341432, 11-109547 and 10-111543 are mentioned.
It is advisable that the thermal development photosensitive material of the present invention contains at least one compound selected from hetero-aromatic mercapto compounds and hetero-aromatic disulfide compounds. Hetero-aromatic mercapto compounds and hetero-aromatic disulfide compounds are described below.
Hetero-aromatic mercapto compounds used in the present invention are preferably compounds represented by the formula Arxe2x80x94SM wherein M is a hydrogen atom or an alkali metal atom, and Ar is an aromatic ring or a fused aromatic ring having at least one nitrogen, sulfur, oxygen, selenium or tellurium atom. Preferable examples of the hetero-aromatic ring include benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine, purine, quinoline and quinazolinone. Benzimidazole, benzothiazole, benzoxazole and benzotetrazole are more preferable. Further, the hetero-aromatic ring may have a substituent selected from, for example, a halogen (for example, Br or Cl), hydroxy, amino, carboxy, alkyl (for example, alkyl having one or more carbon atoms, preferably alkyl having 1 to 4 carbon atoms), alkoxy (for example, alkoxy having one or more carbon atoms, preferably alkoxy having 1 to 4 carbon atoms) and an aryl (which may have a substituent).
Examples of the hetero-aromatic mercapto compounds include 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, 2-mercapto-5-methylbenzimidazole, 6-ethoxy-2-mercaptobenzothiazole, 2,2xe2x80x2-dithiobis(benzothiazole), 3-mercapto-1,2,4-triazole, 4,5-diphenyl-2-imidazolethiol, 2-mercaptoimidazole, 1-ethyl-2-mercaptobenzimidazole, 2-mercaptoquinoline, 8-mercaptopurine, 2-mercapto-4(3H)-quinazolinone, 7-trifluoromethyl-4-quinolinethiol, 2,3,5,6-tetrachloro-4-pyridinethiol, 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate, 2-amino-5-mercapto-1,3,4-thiadiazole, 3-amino-5-mercapto-1,2,4-triazole, 4-hydroxy-2-mercaptopyrimidine, 2-mercaptopyrimidine, 4,6-diamino-2-mercaptopyrimidine, 2-mercapto-4-methylpyrimidine hydrochloride, 3-mercapto-5-phenyl-1,2,4-triazole, 1-phenyl-5-mercaptotetrazole, sodium 3-(5-mercaptotetrazole)benzenesulfonate, N-methyl-Nxe2x80x2-[3-(5-mercaptotetrazolyl)phenyl]urea and 2-mercapto-4-phenyloxazole. However, the present invention is not limited thereto.
The amounts of the hetero-aromatic mercapto compounds are preferably 0.001 to 1 mol, more preferably 0.003 to 0.1 mol, per mol of silver in the emulsion layer. One mol of silver as referred to here means one mol of silver halide.
The hetero-aromatic disulfide compounds are preferably compounds represented by the formula Arxe2x80x94Sxe2x80x94Sxe2x80x94Ar wherein Ar is an aromatic ring or a fused aromatic ring having at least one nitrogen, sulfur, oxygen, selenium or tellurium atom. Preferable examples of the hetero-aromatic ring include benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine, pyridine, purine, quinoline and quinazolinone. Benzimidazole, benzothiazole, benzoxazole and benzotetrazole are more preferable.
The hetero-aromatic ring may have a substituent selected from the group consisting of a halogen (for example, Br or Cl), hydroxy, amino, carboxy, alkyl (for example, alkyl having one or more carbon atoms, preferably alkyl having 1 to 4 carbon atoms), alkoxy (for example, alkoxy having one or more carbon atoms, preferably alkoxy having 1 to 4 carbon atoms) and an aryl (which may have a substituent).
The amounts of the hetero-aromatic disulfide compounds are preferably 0.001 to 1 mol, more preferably 0.003 to 0.1 mol, per mol of silver in the emulsion layer. One mol of silver as referred to here means one mol of silver halide.
A binder used in the present invention is described below.
The organic silver salt-containing layer in the thermal development photosensitive material of the present invention contains the binder. The binder may be any polymer. An appropriate binder is transparent or semitransparent, and generally colorless. Examples include natural resins, synthetic resins, polymers, copolymers and other film-forming mediums such as gelatins, rubbers, poly(vinyl alcohol) types, hydroxyethyl celluloses, cellulose acetates, cellulose acetate butyrates, polyvinylpyrrolidones, casein, starch, polyacrylic acids, polymethyl methacrylates, polyvinyl chlorides, polymethacrylic acids, styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, polyvinyl acetals (for example polyvinyl formal and polyvinyl butyral), polyesters, polyurethanes, phenoxy resins, polyvinylidene chlorides, polyepoxides, polycarbonates, polyvinyl acetates, polyolefins, cellulose esters and polyamides. The binder may be coating-formed with water, an organic solvent or an emulsion.
In the present invention, the glass transition temperature of the binder of the layer containing the organic silver salt is preferably from 10xc2x0 C. to 80xc2x0 C. (hereinafter sometimes referred to as a high Tg binder), more preferably 20xc2x0 C. to 70xc2x0 C., further preferably from 23xc2x0 C. to 65xc2x0 C.
In the present specification, Tg is calculated using the following formula:
1/Tg=xcexa3(Xi/Ti) 
wherein i is 1 to n.
That is, a polymer herein is one obtained by copolymerizing n numbers (from i=1 to i=n) of monomer components. Xi is a weight percent (xcexa3Xi=1) of an i-th monomer, and Tgi is a glass transition temperature (absolute temperature) of a homopolymer of the i-th monomer. xcexa3 is a sum of values from i=1 to i=n. For the value of the glass transition temperature (Tgi) of a homopolymer of each monomer, a value in Polymer Handbook (3rd Edition, J. Brandrup, E. H. Immergut, Wiley-Interscience, 1989) can be employed.
As the binder, these polymers may be used either singly or in combination. Further, a combination of a polymer having a glass transition temperature of 20xc2x0 C. or more and a polymer having a glass transition temperature of less than 20xc2x0 C. may be used. When two or more polymers different in Tg are used by being blended, the weight average Tg thereof is preferably in the aforementioned ranges.
In the present invention, performance is improved when the organic silver salt-containing layer is formed by coating a coating solution in which at least 30% by mass of the solvent is water, and drying the same, and further improved when the binder of the organic silver salt-containing layer is soluble or dispersible in an aqueous solvent, and especially when the binder is formed of a latex of a polymer in which an equilibrium water content at 25xc2x0 C., 60% RH is 2% by mass or less. Most preferable is that the binder is formed such that ionic conductivity is 2.5 mS/cm or less. As a method therefor, a method in which, after a polymer is formed, it is purified using a separation film is mentioned.
The aqueous solvent in which the polymer is soluble or dispersible as referred to here means water or a mixture of water and 70% by mass or less of a water-miscible organic solvent. Examples of the water-miscible organic solvent include alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol, cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve, ethyl acetate and dimethylformamide.
In cases of a system in which the polymer is not dissolved thermodynamically but is present in a so-called dispersed state, the term xe2x80x9caqueous solventxe2x80x9d is also applied thereto.
Further, the xe2x80x9cequilibrium water content at 25xc2x0 C., 60% RHxe2x80x9d is represented by the following formula, using a weight w1 of the polymer in moisture equilibrium under an atmosphere of 25xc2x0 C. and 60% RH and a weight w0 of the polymer in an absolute dry state at 25xc2x0 C.
Equilibrium water content at 25xc2x0 C. and 60% RH =((w1xe2x88x92w0)/w0)xc3x97100(% by mass)) 
With respect to the definition of the water content and the method of measuring the same, for example, Kobunshi Kogaku Koza 14 and Kobunshi Zairyo Shikenho (compiled by Kobunshi Gakkai and Chijin Shokan) can be referred to.
The equilibrium water content at 25xc2x0 C. and 60% RH of the binder polymer in the present invention is preferably 2% by mass or less, more preferably from 0.01% by mass to 1.5% by mass, and further preferably from 0.02% by mass to 1% by mass.
In the present invention, a polymer dispersible in the aqueous solvent is most preferable. Examples of the dispersed state include a latex in which fine particles of a water-insoluble hydrophobic polymer are dispersed, and a state in which polymer molecules are dispersed in a molecular state or by forming micelles. Both cases are preferable. The average particle diameter of the dispersed particles is preferably 1 nm to 50,000 nm, more preferably 5 nm to 1,000 nm. Particle size distribution of the dispersed particles is not particularly limited. A wide particle size distribution and a monodisperse particle size distribution are both usable.
In the present invention, preferable examples of the polymer dispersible in the aqueous solvent can include hydrophobic polymers such as acrylic polymers, polyesters, rubbers (for example, an SBR resin), polyurethanes, polyvinyl chlorides, polyvinyl acetates, polyvinylidene chlorides and polyolefins. These polymers may be linear polymers, branched polymers and crosslinked polymers. So-called homopolymers obtained by polymerizing single monomers and copolymers obtained by polymerizing two or more monomers are also usable. In the case of copolymers, random copolymers and block copolymers are usable. It is advisable that the molecular weight of these polymers is 5,000 to 1,000,000, preferably 10,000 to 200,000, in terms of number average molecular weight. When the number average molecular weight is 5,000 to 1,000,000, a satisfactory dynamic strength of an emulsion layer and good film formability can be obtained.
Preferable examples of a polymer latex are shown below. In the following list, the polymer latex is shown by starting monomers, the parenthesized value is % by mass, and the molecular weight is a number average molecular weight. In cases of using a polyfunctional monomer, the concept of molecular weight cannot be used because a crosslinked structure is formed. Thus, xe2x80x9ccrosslinkedxe2x80x9d is shown, and description of the molecular weight is omitted. Tg indicates a glass transition temperature.
P-1: MMA(70)-EA(27)-MAA(3) latex (molecular weight 37,000)
P-2: MMA(70)-2EHA(20)-St(5)-AA(5) latex (molecular weight 40,000)
P-3: St(50)-Bu(47)-MAA(3) latex (crosslinked)
P-4: St(68)-Bu(29)-AA(3) latex (crosslinked)
P-5: St(71)-Bu(26)-AA(3) latex (crosslinked, Tg 24xc2x0 C.)
P-6: St(70)-Bu(27)-IA(3) latex (crosslinked)
P-7: St(75)-Bu(24)-AA(1) latex (crosslinked)
P-8: St(60)-Bu(35)-DVB(3)-MAA(2) latex (crosslinked)
P-9: St(70)-Bu(25)-DVB(2)-AA(3) latex (crosslinked)
P-10: VC(50)-MMA(20)-EA(20)-AN(5)-AA(5) latex (molecular weight 80,000)
P-11: VDC(85)-MMA(5)-EA(5)-MAA(5) latex (molecular weight 67,000)
P-12: Et(90)-MMA(10) latex (molecular weight 12,000)
P-13: St(70)-2EHA(27)-AA(3) latex (molecular weight 130,000)
P-14: MMA(63)-EA(35)-AA(2) latex (molecular weight 33,000)
P-15: St(70.5)-Bu(26.5)-AA(3) latex (crosslinked, Tg 23xc2x0 C.)
P-16: St(69.5)-Bu(27.5)-AA(3) latex (crosslinked, Tg 20.5xc2x0 C.)
The abbreviations in the above structures indicate the following monomers.
MMA: methyl methacrylate
EA: ethyl acrylate
MAA: methacrylic acid
2EHA: 2-ethylhexyl acrylate
St: styrene
Bu: butadiene
AA: acrylic acid
DVB: divinylbenzene
VC: vinyl chloride
AN: acrylonitrile
VDC: vinylidene chloride
Et: ethylene
IA: itaconic acid
The polymer latexes listed above are commercially usable, and the following polymers can be utilized. Examples of the acrylic polymers include SEVIAN A-4635, 4718 and 4601 (manufactured by Daicel Chemical Industries, Ltd.), and NIPOL Lx 811, 814, 821, 820 and 857 (manufactured by Nippon Zeon Co., Ltd.). Examples of the polyesters include FINETEX ES 650, 611, 675 and 850 (manufactured by Dainippon Ink And Chemicals, Inc.), and WD-size WMS (manufactured by Eastman Chemical). Examples of the polyurethanes include HYDRAN AP 10, 20, 30 and 40 (manufactured by Dainippon Ink And Chemicals, Inc.). Examples of the rubbers include LACSTAR 7310K, 3307B, 4700H and 7132C (manufactured by Dainippon Ink And Chemicals, Inc.), and NIPOL Lx 416, 410, 438C and 2507 (manufactured by Nippon Zeon Co., Ltd.). Examples of the polyvinyl chloride series include G350 and G576 (manufactured by Nippon Zeon Co., Ltd.). Examples of the polyvinylidene chloride series include L502 and L513 (manufactured by Asahi Chemical Industry Co., Ltd.). Examples of the polyolefins include CHEMIPEARL S120 and SA100 (manufactured by Mitsui Petrochemical Industries, Ltd.).
These polymer latexes may be used either singly or by blending two or more types as required.
As the polymer latex used in the present invention, a styrene-butadiene copolymer latex is especially preferable. The weight ratio of styrene monomer units and butadiene monomer units in the styrene-butadiene copolymer is preferably from 40:60 to 95:5. The ratio that the styrene monomer units and the butadiene monomer units occupy in the copolymer is preferably 60 to 99% by mass. The preferable range of molecular weight is the same as mentioned above.
As the styrene-butadiene copolymer latex used in the present invention, P-3 to P-8, P-14, P-15, and commercial products LACSTAR-3307B, LACSTAR-7132C and NIPOL Lx 416 are mentioned.
The organic silver salt-containing layer of the photosensitive material in the present invention may contain, as required, hydrophilic polymers such as gelatin, polyvinyl alcohol, methyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose. The amount of the hydrophilic polymers is preferably 30% by mass or less, more preferably 20% by mass or less, based on the total binder of the organic silver salt-containing layer.
The organic silver salt-containing layer (the imaging layer) of the present invention is preferably formed by using the polymer latex. For the amount of the binder in the organic silver salt-containing layer, a total binder/organic silver salt weight ratio is from 1/10 to 10/1, preferably 1/5 to 4/1.
This organic silver salt-containing layer is usually a photosensitive layer (emulsion layer) containing photosensitive silver halide as the photosensitive silver salt. In this case, the total binder/silver halide weight ratio is preferably 400 to 5, more preferably 200 to 10.
The total amount of the binder in the imaging layer of the present invention is preferably 0.2 to 30 g/m2, more preferably 1 to 15 g/m2. The imaging layer of the present invention may contain a crosslinking agent for crosslinking and a surfactant for improving coating property.
Other components contained in the thermal development photosensitive material of the present invention are described below.
A solvent (for simplicity, solvents and dispersion media are here referred to in common as xe2x80x9ca solventxe2x80x9d) of the organic silver salt-containing layer coating solution of the photosensitive material in the present invention may be an aqueous solvent containing 30% by mass or more of water. As a component other than water, any water-miscible organic solvent may be used, examples thereof being methyl alcohol, ethyl alcohol, isopropyl alcohol, methyl cellosolve, ethyl cellosolve, dimethylformamide and ethyl acetate. The water content of the solvent in the coating solution is preferably 50% by mass or more, more preferably 70% by mass or more. Examples of preferable solvent compositions include, other than just water, water/methyl alcohol=90/10, water/methyl alcohol=70/30, water/methyl alcohol/dimethylformamide=80/15/5, water/methyl alcohol/ethyl cellosolve=85/10/5 and water/methyl alcohol/isopropyl alcohol=85/10/5 (numerical values are % by mass).
Examples of an antifogging agent, a stabilizer and a stabilizer precursor that can be used in the present invention include those described in JP-A No. 10-62899, paragraph [0070], European Patent Laid-Open No. 0803764A1, page 20, line 57 to page 21, line 7, and compounds described in JP-A Nos. 9-281637 and 9-329864. Antifogging agents preferably used in the present invention include organic halides, and compounds described in JP-A No. 11-65021, paragraphs [0111] and [0112], are mentioned. Especially, organic halogen compounds represented by formula (P) in Japanese Patent Application No. 11-87297, organic polyhalogen compounds represented by formula (II) in JP-A No. 10-339934, and organic polyhalogen compounds described in Japanese Patent Application No. 11-205330 are preferable.
The preferable organic polyhalogen compounds of the present invention are specifically described below. The preferable organic polyhalogen compounds of the present invention are compounds represented by formula (P).
Qxe2x80x94(Y)nxe2x80x94C(Z1) (Z2)X xe2x80x83xe2x80x83Formula (P) 
Q represents an alkyl group, an aryl group or a heterocyclic group. Y represents a divalent binding group. n represents 0 or 1. Z1 and Z2 each represents a halogen atom, and X represents a hydrogen atom or an electron-attractive group.
In formula (P), Q represents preferably a phenyl group substituted with an electron-attractive group of which a Hammett substituent constant "sgr"p is a positive value. With respect to the Hammett substituent constant, Journal of Medicinal Chemistry, 1973, vol. 16, No. 11, pp. 1207 to 1216, and the like can be referred to. Examples of the electron-attractive group include halogen atoms (for example, a fluorine atom ("sgr"p: 0.06), a chlorine atom ("sgr"p: 0.23), a bromine atom ("sgr"p: 0.23) or an iodine atom ("sgr"p: 0.18)), a trihalomethyl group (tribromomethyl ("sgr"p: 0.29), trichloromethyl ("sgr"p: 0.33) or trifluoromethyl ("sgr"p: 0.54)), a cyano group ("sgr"p: 0.66), a nitro group ("sgr"p: 0.78), an aliphatic aryl or heterocyclic sulfonyl group (for example, methanesulfonyl ("sgr"p: 0.72)), an aliphatic aryl or heterocyclic acyl group (for example, acetyl ("sgr"p: 0.50) or benzoyl ("sgr"p: 0.43)), an alkinyl group (for example, Cxe2x89xa1CH ("sgr"p: 0.23)), an aliphatic aryl or heterocyclic oxycarbonyl group (for example, methoxycarbonyl ("sgr"p: 0.45) or phenoxycarbonyl ("sgr"p: 0.44)), a carbamoyl group ("sgr"p: 0.36), a sulfamoyl group ("sgr"p: 0.57), a sulfoxide group, a heterocyclic group and a phosphoryl group. "sgr"p is preferably 0.2 to 2.0, and more preferably 0.4 to 1.0. Especially preferable as the electron-attractive group are a carbamoyl group, an alkoxycarbonyl group, an alkylsulfonyl group and an alkyphosphoryl group. Of these, a carbamoyl group is most preferable.
X is preferably an electron-attractive group, more preferably a halogen atom, an aliphatic aryl or heterocyclic sulfonyl group, an aliphatic aryl or heterocyclic acyl group, an aliphatic aryl or heterocyclic oxycarbonyl group, a carbamoyl group, or a sulfamoyl group. A halogen atom is especially preferable. As the halogen atom, a chlorine atom, a bromine atom and an iodine atom are preferable. A chlorine atom and a bromine atom are further preferable. A bromine atom is especially preferable.
Y is preferably xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94SOxe2x80x94 or xe2x80x94SO2xe2x80x94. xe2x80x94C(xe2x95x90O)xe2x80x94 and xe2x80x94SO2xe2x80x94 are more preferable, and xe2x80x94SO2xe2x80x94 is especially preferable. n represents 0 or 1, and 1 is preferable.
Specific examples of the compounds of formula (P) in the present invention are listed below. 
The compound represented by formula (P) in the present invention is used in an amount of preferably 10xe2x88x924 to 1 mol, more preferably 10xe2x88x923 to 0.8 mol, further preferably 5xc3x9710xe2x88x923 to 0.5 mol, per mol of the non-photosensitive silver salt of the imaging layer.
In the present invention, as a method of incorporating the antifogging agent in the photosensitive material, the method of incorporating the reducing agent described earlier can be mentioned.
Examples of the antifogging agent include mercury (II) salts in JP-A No. 11-65021, paragraph [0113], benzoic acids in the same document, paragraph [0114], salicylic acid derivatives in JP-A No. 2000-206642, formalin scavenger compounds represented by formula (S) in JP-A No. 2000-221634, triazine compounds in claim 9 of JP-A No. 11-352642, compounds represented by formula (III) in JP-A No. 6-11791 and 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene.
The thermal development photosensitive material of the present invention may contain an azolium salt for preventing fogging. Examples of the azolium salt include compounds of formula (XI) described in JP-A No. 59-193447, compounds described in Japanese Patent Publication No. 55-12581 and compounds of formula (II) described in JP-A No. 60-153039. The azolium salt may be added to any part of the photosensitive material. As a layer to which the azolium salt is added, it is preferable to add the azolium salt to a layer on a surface having the photosensitive layer. It is more preferable to add the azolium salt to the organic silver salt-containing layer. The addition of the azolium salt may be conducted at any step of preparing a coating solution. When the azolium salt is added to the organic silver salt-containing layer, addition may be conducted at any step from the preparation of the organic silver salt to the preparation of the coating solution. It is preferable to conduct the addition from after the preparation of the organic silver salt till just before coating. The azolium salt can be added in the form of a powder, a solution or a fine grain dispersion. Further, it may be added as a solution containing other additives, such as a sensitization coloring matter, a reducing agent and a color matching agent. In the present invention, the amount of the azolium salt is not particularly limited. It is preferably from 1xc3x9710xe2x88x926 mol to 2 mols, more preferably from 1xc3x9710xe2x88x923 mol to 0.5 mol, per mol of silver.
It is advisable that a color matching agent is added to the thermal development photosensitive material of the present invention. The color matching agent is described in JP-A No. 10-62899, paragraphs [0054] and [0055], European Patent Laid-Open No. 0803764A1, page 21, lines 23 to 48, JP-A No. 2000-356317 and Japanese Patent Application No. 2000-187298. Especially preferable are phthalazinones (phthalazinone and phthalazinone derivatives or metal salts such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone and 2,3-dihydro-1,4-phthalazinedione), combinations of phthalazinones and phthalic acids (such as phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, diammonium phthalate, sodium phthalate, potassium phthalate and tetrachlorophthalic anhydride), phthalazines (phthalazine and phthalazine derivatives or metal salts such as 4-(1-naphthyl)phthalazine, 6-isopropylphthalazine, 6-t-butylphthalazine, 6-chlorophthalazine, 5,7-dimethoxyphthalazine and 2,3-dihydrophthalazine), and combinations of phthalazines and phthalic acids. Especially, combinations of phthalazines and phthalic acids are preferable.
A plasticizer and a lubricant that can be used in the photosensitive layer of the present invention are described in JP-A No. 11-65021, paragraph [0117]. As a superhigh contrast agent for superhigh contrast imaging, a method of adding the same and an amount, compounds of formula (H), compounds of formulas (1) to (3) and compounds of formulas (A) and (B) are described in JP-A No. 11-65021, paragraph [0118], JP-A No. 11-223898, paragraphs [0136] to [0193], and Japanese Patent Application No. 11-87297, respectively, and compounds of formulas (III) to (V) are described in Japanese Patent Application No. 11-91652 (specifically, compounds of formulas 21 to 24). A superhigh contrast accelerator is described in JP-A No. 11-65021, paragraph [0102], and JP-A No. 11-223898, paragraphs [0194] and [0195].
When formic acid or a formic acid salt is used as a strong blushing material, it is advisable to incorporate the same in the imaging layer containing the photosensitive silver halide in an amount of, preferably, 5 mmols or less, more preferably 1 mmol or less, per mol of silver.
When a superhigh contrast agent is used in the thermal development photosensitive material of the present invention, it is advisable to use an acid obtained by hydrating diphosphorus pentoxide or a combination of salts thereof. Examples of an acid obtained by hydrating diphosphorus pentoxide or salts thereof can include metaphosphoric acid (salt), pyrophosphoric acid (salt), orthophosphoric acid (salt), triphosphoric acid (salt), tetraphosphoric acid (salt) and hexametaphosphoric acid (salt). Especially preferable examples of the acid obtained by hydrating diphosphorus pentoxide or salts thereof can include orthophosphoric acid (salt) and hexametaphosphoric acid (salt). Specific examples of the salt include sodium orthophosphate, sodium dihydrogenorthophosphate, sodium hexametaphosphate and ammonium hexametaphosphate.
The amount of the acid obtained by hydrating diphosphorus pentoxide or its salt (coating amount for 1 m2 of the photosensitive material) may be a desired amount according to properties such as sensitivity and fogging. It is preferably 0.1 to 500 mg/m2, more preferably 0.5 to 100 mg/m2.
In the thermal development photosensitive material of the present invention, a surface protecting layer can be formed for preventing adhesion of the imaging layer. The surface protecting layer may be a single layer or plural layers. The surface protecting layer is described in JP-A No. 11-65021, paragraphs [0119] and [0120], and Japanese Patent Application No. 2000-171936.
As a binder of the surface protecting layer in the present invention, gelatin is preferable. It is advisable that polyvinyl alcohol (PVA) is used alone or in combination. As the gelatin, inert gelatin (for example, Nitta Gelatin 750) and phthalic gelatin (for example, Nitta Gelatin 801) can be used. As PVA, those described in JP-A No. 2000-171936, paragraphs [0009] to [0020], are mentioned. Preferable examples thereof include completely saponified polyvinyl alcohol PVA-105, partially saponified polyvinyl alcohols PVA-205 and PVA-335 and modified polyvinyl alcohol MP-203 (manufactured by Kuraray Co., Ltd.). The coating amount (for 1 m2 of a substrate) of polyvinyl alcohol of the protecting layer (for one layer) is preferably 0.3 to 4.0 g/m2, more preferably 0.3 to 2.0 g/m2.
When the thermal development photosensitive material of the present invention is used in printing that involves problems of dimensional variations, it is advisable to use a polymer latex in a surface protecting layer or a back layer. Such a polymer latex is described in xe2x80x9cGoseijushi Emarujonxe2x80x9d (compiled by Okuda H. and Inagaki H., published by Kobunshi Kankokai (1978)), xe2x80x9cGosei Ratekkusu No Oyoxe2x80x9d (compiled by Sugimura H., Kataoka Y., Suzuki S. and Kasahara K., published by Kobunshi Kankokai (1993)), and xe2x80x9cGosei Ratekkusu No Kagakuxe2x80x9d (compiled by Muroi S., published by Kobunshi Kankokai (1970)). Specific examples thereof include a methyl methacrylate (33.5% by mass)/ethyl acrylate (50% by mass)/methacrylic acid (16.5% by mass) copolymer latex, a methyl methacrylate (47.5% by mass)/butadiene (47.5% by mass)/itaconic acid (5% by mass) copolymer latex, an ethyl acrylate/methacrylic acid copolymer latex, a methyl methacrylate (58.9% by mass)/2-ethylhexyl acrylate (25.4% by mass)/styrene (8.6% by mass)/2-hydroxyethyl methacrylate (5.1% by mass)/acrylic acid (2.0% by mass) copolymer latex, and a methyl methacrylate (64.0% by mass)/styrene (9.0% by mass)/butyl acrylate (20.0% by mass)/2-hydroxyethyl methacrylate (5.0% by mass)/acrylic acid (2.0% by mass) copolymer latex. Further, as a binder for the surface protecting layer, a combination of polymer latexes in Japanese Patent Application No. 11-6872, a technique described in Japanese Patent Application No. 11-143058, paragraphs [0021] to [0025], a technique described in Japanese Patent Application No. 11-6872, paragraphs [0027] and [0028], and a technique described in Japanese Patent Application No. 10-199626, paragraphs [0023] to [0041], may be employed. The ratio of polymer latex in the surface protecting layer is preferably at least 10% by mass to 90% by mass, more preferably at least 20% by mass to 80% by mass based on the total binder.
The coating amount (for 1 m2 of the substrate) of the total binder (comprising the water-soluble polymer and the latex polymer) based on the surface protecting layer (for one layer) is preferably 0.3 to 5.0 g/m2, more preferably 0.3 to 2.0 g/m2.
A temperature at which to prepare the imaging layer coating solution of the present invention is preferably from 30xc2x0 C. to 65xc2x0 C., more preferably from 35xc2x0 C. to 60xc2x0 C., further preferably from 35xc2x0 C. to 55xc2x0 C. Further, it is advisable that the temperature of the imaging layer coating solution just after the addition of the polymer latex is maintained at from 30xc2x0 C. to 65xc2x0 C.
An image-forming method using the thermal development photosensitive material of the present invention is described below.
As the imaging layer of the present invention, one or more layers are formed on the substrate. When the imaging layer is made of one layer, that layer comprises the organic silver salt, the photosensitive silver halide, the reducing agent for silver ions and the binder, and, as required, contains additives such as a color matching agent, a coating aid and other aids. When the imaging layer is made of two or more layers, it is required that a first imaging layer (usually a layer adjacent to the substrate) contains the organic silver salt and the photosensitive silver halide and a second imaging layer, or both layers, contains other components. A multicolor photosensitive thermal development photographic material may include a combination of two such layers for each color, or all components may be contained in a single layer as described in U.S. Pat. No. 4,708,928. In the case of a multi-dye, multicolor photosensitive thermal development photographic material, emulsion layers are generally arranged separately from each other by functional or non-functional barrier layers between photosensitive layers, as described in U.S. Pat. No. 4,460,681.
In the photosensitive layer of the present invention, various dyes or pigments (for example, C. I. Pigment Blue 60, C. I. Pigment Blue 64 and C. I. Pigment Blue 15:6) can be used in view of tone improvement, prevention of occurrence of interference fringes in laser exposure and prevention of irradiation. These are described in detail in WO 98/36322 and JP-A Nos. 10-268465 and 11-338098.
In the thermal development photosensitive material of the present invention, an antihalation layer can be formed on the photosensitive layer at the side thereof to be further from a light source.
The thermal development photosensitive material generally has a non-photosensitive layer in addition to the photosensitive layer. Non-photosensitive layers can be classified by location into (1) a protecting layer formed on the photosensitive layer (remote from the substrate), (2) an intermediate layer formed between plural photosensitive layers or between the photosensitive layer and the protecting layer, (3) an undercoat layer formed between the photosensitive layer and the substrate and (4) a back layer formed at a side of the substrate opposite to the photosensitive layer. A filter layer is formed on the photosensitive layer as a layer (1) or (2). An antihalation layer is formed on the photosensitive material as a layer of type (3) or (4).
The antihalation layer is described in JP-A No. 11-65021, paragraphs [0123] and [0124], and JP-A Nos. 11-223898, 9-230531, 10-36695, 10-104779, 11-231457, 11-352625 and 11-352626.
The antihalation layer contains an antihalation dye having absorption at an exposure wavelength. When the exposure wavelength is in the infrared region, an infrared absorption dye may be used, and a dye having absorption in the visible region is preferable.
When halation is prevented by using a dye having absorption in the visible region, it is preferable that color of the dye substantially does not remain after imaging, and that a method of erasing the color with heat in the thermal development is used. It is especially preferable that a non-photosensitive layer functions as an antihalation layer by adding thereto a heat-erasable dye and a basic precursor. These techniques are described in JP-A No. 11-231457.
The amount of the erasable dye is determined depending on usage of the dye. Generally, the dye is used in such an amount that optical density (absorbance) when measured at the intended wavelength exceeds 0.1. The optical density is preferably 0.2 to 2. An amount of the dye for obtaining such an optical density is generally 0.001 to 1 g/m2.
When the dye is erased in this manner, the optical density after thermal development can be decreased to 0.1 or less. Two or more erasable dyes may be used in combination in a heat-erasable recording medium or a thermal development photosensitive material. Likewise, two or more of the basic precursors may be used in combination.
In the heat-erasing with the erasable dye and the basic precursor, it is advisable, in view of heat erasability, to use a material which decreases a melting point by more than 3xc2x0 C. in combination with the basic precursor, as described in JP-A No. 11-352626 (for example, diphenylsulfone and 4-chlorophenyl(phenyl)sulfone).
In the present invention, a colorant having maximum absorption at 300 to 450 nm can be added to improve silver tone and change of an image with time. Such a colorant is described in JP-A Nos. 62-210458, 63-104046, 63-103235, 63-208846, 63-306436, 63-314535, 1-61745 and 11-276751.
This colorant is usually added in an amount of 0.1 mg/m2 to 1 g/m2. A layer to which the colorant is added is preferably the back layer formed opposite the photosensitive layer.
The thermal development photosensitive material in the present invention is preferably a single-sided photosensitive material having a photosensitive layer containing the at least one silver halide emulsion layer on one side of the substrate and the back layer on another side thereof.
In the present invention, it is advisable to add a matt agent for improving a transportability. The matt agent is described in JP-A No. 11-65021, paragraphs [0126] and [0127]. An amount of the matt agent is preferably 1 to 400 mg/m2, more preferably 5 to 300 mg/m2, in terms of a coating amount for 1 m2 of the photosensitive material.
Any matt degree of the emulsion surface providing xe2x80x9cstardustxe2x80x9d flaws do not occur. Bekk smoothness is preferably from 30 seconds to 2,000 seconds, more preferably from 40 seconds to 1,500 seconds. The Bekk smoothness can easily be measured as in JIS P 8119, xe2x80x9cSmoothness Test Method of Paper and Board with a Bekk Testerxe2x80x9d and TAPPI Standard Method T479.
In the present invention, for matt degree of the back layer, the Bekk smoothness is preferably at most 1,200 seconds and at least 10 seconds, more preferably at most 800 seconds and at least 20 seconds, and further preferably at most 500 seconds and at least 40 seconds.
In the present invention, it is advisable that the matt agent is incorporated in an outermost surface layer or a layer that functions as an outermost surface layer of the photosensitive material, or in a layer close to the outermost surface, or in a layer that functions as a protecting layer.
A back layer that can be used in the present invention is described in JP-A No. 11-65021, paragraphs [0128] to [0130].
In the thermal development photosensitive material of the present invention, the pH of the film surface before thermal development is preferably 7.0 or less, more preferably 6.6 or less. Although a lower limit is not particularly specified, it is approximately 3. The most preferable pH range is 4 to 6.2. It is advisable, in view of decreasing the pH of the film surface, that the pH of the film surface is adjusted with organic acids such as phthalic acid derivatives, non-volatile acids such as sulfuric acid, or volatile bases such as ammonia. Especially, ammonia is preferable for attaining a low pH of the film surface because it is easily volatilized and can be removed before the coating step or thermal development. Further, a combination with a non-volatile base such as sodium hydroxide, potassium hydroxide or lithium hydroxide and ammonia is preferably used. A method of measuring pH of a film surface is described in Japanese Patent Application No. 11-87297, paragraph [0123].
A hardening agent may be used in the photosensitive layer, the protecting layer and the back layer of the present invention. Examples of the hardening agent are described in T. H. James, xe2x80x9cThe Theory Of The Photographic Process, Fourth Editionxe2x80x9d (Macmillan Publishing Co., Inc., 1977), pp. 77-87. Preferable examples thereof include chrome alum, 2,4-dichloro-6-hydroxy-s-triazine sodium salt, N,N-ethylenebis(vinylsulfonacetamide), N,N-propylenebis(vinylsulfonacetamide), polyvalent metallic ions as shown on page 78 of the above document, polyisocyanates described in U.S. Pat. No. 4,281,060 and JP-A No. 6-208193, epoxy compounds described in U.S. Pat. No. 4,791,042 and vinylsulfone compounds described in JP-A No. 62-89048.
The hardening agent is added as a solution, and a time for adding the solution into a protecting layer coating solution is from 180 minutes before coating till just before coating, preferably from 60 minutes to 10 seconds before coating. A mixing method and mixing conditions are not particularly limited so long as the effects of the present invention are satisfactorily brought forth. Specific examples of the mixing method include a method using a tank in which an average retention time, calculated from an addition feed rate and an amount of a solution fed to a coater, becomes a desired time, and a method using a static mixer as described in chapter 8 of xe2x80x9cLiquid Mixing Technologyxe2x80x9d, N. Harnby, M. F. Edwards and A. W. Nienow, translated by Takahashi K. (Nikkan Kogyo Shinbunsha, 1989).
A surfactant which can be used in the present invention is described in JP-A No. 11-65021, paragraph [0132], a solvent in the same document, paragraph [0133], a substrate in the same document, paragraph [0134], an antistatic or conductive layer in the same document, paragraph [0135], a method of obtaining a color image in the same document, paragraph [0136], and a lubricant in JP-A No. 11-84573, paragraphs [0061] to [0064], and Japanese Patent Application No. 11-106881, paragraphs [0049] to [0062].
In a transparent substrate, a polyester, especially polyethylene terephthalate, which is heat-treated at a temperature of 130xc2x0 C. to 185xc2x0 C. is preferably used for relaxing internal strain remaining in the film in biaxial stretching and eliminating heat shrinkage strain generated during the thermal development. In the case of a thermal development photosensitive material for medical use, the transparent substrate may be colored with a blue dye (for example, dye-1 described in the Examples of JP-A No. 8-240877) or may be colorless. It is advisable that an undercoating technique of a water-soluble polyester in JP-A No. 11-84574, a styrene-butadiene copolymer in JP-A No. 10-186565 and a vinylidene chloride copolymer in JP-A No. 2000-39684 and Japanese Patent Application No. 11-106881, paragraphs [0063] to [0080], are applied to the substrate. Further, for an antistatic layer or undercoating, a technique described in JP-A Nos. 56-143430, 56-143431, 58-62646, 56-120519 and 11-84573, paragraphs [0040] to [0051], U.S. Pat. No. 5,575,957 and JP-A No. 11-223898, paragraphs [0078] to [0084], can be applied.
The thermal development photosensitive material is preferably of a mono-sheet type (a type with which an image can be formed on the thermal development photosensitive material without using another sheet, such as an image-receiving material).
The thermal development photosensitive material may further contain an antioxidant, a stabilizer, a plasticizer, an ultraviolet absorber and a coating aid. These additives are added to either the photosensitive layer or the non-photosensitive layer. With respect to these additives, WO 98/36322, EP 803764A1 and JP-A Nos. 10-186567 and 10-18568 can be referred to.
The thermal development photosensitive material in the present invention may be coated by any method. Specific examples of coating methods include various coating methods such as extrusion coating, slide coating, curtain coating, dip coating, knife coating, flow coating and extrusion coating with a hopper as described in U.S. Pat. No. 2,681,294. Extrusion coating or slide coating as described by Stephen F. Kistler and Peter M. Schweizer, xe2x80x9cLiquid Film Coatingxe2x80x9d, Chapman and Hall, 1997, pp. 399-536 is preferable. Slide coating is especially preferable. An example of the form of a slide coater used in the slide coating is shown in FIG. 11b.1 on page 427 of the same document. Further, it is also possible, if required, to coat two or more layers at the same time by the method described in the same document, pages 399 to 536, U.S. Pat. No. 2,761,791 and British Patent No. 837,095.
The organic silver salt-containing layer coating solution in the present invention is preferably a so-called thixotropic fluid. With regard thereto, JP-A No. 11-52509 can be referred to. For the organic silver salt-containing layer coating solution in the present invention, viscosity at a shear rate of 0.1 sxe2x88x921 is preferably from 400 mPa.s to 100,000 mPa.s, more preferably from 500 mPa.s to 20,000 mPa.s. Further, viscosity at a shear rate of 1,000 sxe2x88x921 is preferably from 1 mPa.s to 200 mPa.s, more preferably from 5 mPa.s to 80 mPa.s.
Technology that can be used for the thermal development photosensitive material of the present invention is described in EP 803764A1, EP 883022A1, WO 98/36322 and JP-A Nos. 56-62648, 58-62644, 9-43766, 9-281637, 9-297367, 9-304869, 9-311405, 9-329865, 10-10669, 10-62899, 10-69023, 10-186568, 10-90823, 10-171063, 10-186565, 10-186567, 10-186569 to 10-186572, 10-197974, 10-197982, 10-197983, 10-197985 to 10-197987, 10-207001, 10-207004, 10-221807, 10-282601, 10-288823, 10-288824, 10-307365, 10-312038, 10-339934, 11-7100, 11-15105, 11-24200, 11-24201, 11-30832, 11-84574, 11-65021, 11-109547, 11-125880, 11-129629, 11-133536 to 11-133539, 11-133542, 11-133543, 11-223898, 11-352627, 11-305377, 11-305378, 11-305384, 11-305380, 11-316435, 11-327076, 11-338096, 11-338098, 11-338099, 11-343420, 2000-187298, 2000-10229, 2000-47345, 2000-206642, 2000-98530, 2000-98531, 2000-112059, 2000-112060, 2000-112104, 2000-112064 and 2000-171936.
The thermal development photosensitive material of the present invention may be developed by any method. Usually, the thermal development photosensitive material is exposed imagewise and developed by heating. A developing temperature is preferably 80 to 250xc2x0 C., and more preferably 100xc2x0 C. to 140xc2x0 C. A developing time is preferably 1 to 60 seconds, more preferably 3 to 30 seconds, especially preferably 5 to 20 seconds, and most preferably 10 to 15 seconds.
A thermal development system is preferably a plate heater system. As the thermal development system with a plate heater, a system described in JP-A No. 11-133572 is preferable. This is a thermal development apparatus in which a visible image is obtained by contacting the thermal development photosensitive material having a latent image formed thereon with a heating unit through a thermal development section. The heating unit comprises the plate heater and plural pressing rollers mounted opposite to one surface of the plate heater, and the thermal development photosensitive material is passed between the pressing rollers and the plate heater to conduct the thermal development. It is advisable that the plate heater is divided into 2 to 6 stages and a temperature of a distal portion is decreased by 1 to 10xc2x0 C. Such a method is described in JP-A No. 54-30032, can remove moisture or an organic solvent contained in the thermal development photosensitive material to outside the system, and can control a change in the shape of the substrate of the thermal development photosensitive material that is caused by abrupt heating of the thermal development photosensitive material.
The photosensitive material of the present invention may be exposed by any method. A laser having an exposure wavelength of 750 nm to 1,400 nm is preferable as an exposure light source. Preferable examples of the laser in the present invention include a gas laser, a YAG laser, a dye laser and a semiconductor laser. Further, a semiconductor laser and a second harmonic-generating element can also be used. Especially preferable is an infrared emission semiconductor laser.
The thermal development photosensitive material of the present invention forms a monochromic image by a silver image, and can be preferably used as a thermal development photosensitive material for medical diagnostics, industrial photography, printing or COM.